A conventional throttle control device for an internal combustion engine is disclosed in U.S. Pat. No. 6,543,417B2 (JP-A-2002-371866). The throttle control device includes a throttle body, a throttle valve, and an engine control device. The throttle body defines therein a throttle bore having a circular-shaped cross section. The throttle valve is rotated by a motor to open and close an intake passage. The engine control device operates the motor in accordance with an accelerator position to control an opening degree of the throttle valve to be in a predetermined opening degree, so that engine control device controls engine speed.
As shown in FIGS. 13, 14, a conventional intake control device for an internal combustion engine includes a throttle body 101, a butterfly type throttle valve (not shown), a shaft 102, a power unit, a coil spring (not shown), and an engine control device (not shown). The butterfly type throttle valve opens and closes a throttle bore of the throttle body 101. The shaft 102, which is in a round bar shape, supports the throttle valve. The power unit operates the throttle valve in the opening direction or the closing direction. The coil spring biases the throttle valve in the closing direction. The engine control device operates a motor (not shown) in accordance with an accelerator position to control the angular position of the throttle valve to be in a predetermined position.
The power unit, which opens and closes the throttle valve, is constructed of a motor (drive source) and a power transmission mechanism (reduction gear). The power transmission mechanism is accommodated in a gearbox 103 connected with the throttle body 101. The reduction gear is constructed of a pinion gear 104 fixed to an output shaft of the motor, an intermediate reduction gear 105 engaging with the pinion gear 104, and a valve gear 106 engaging with the intermediate reduction gear 105. A throttle sensor is mounted to the gearbox 103 to detect an angular position of the throttle valve, that is, a throttle opening degree. The throttle sensor includes a permanent magnet (not shown) fixed to the inner periphery of the valve gear 106, and a non-contact type magnetism detecting element (not shown) that generates an electromotive force in response to a magnetic field generated by the permanent magnet. The non-contact type magnetism detecting element is fixed to a sensor mount part (not shown) of a sensor cover, which closes an opening side of the gearbox 103 of the throttle body 101, in a manner to be arranged in opposition to the inner peripheral surface of a yoke, which is magnetized by the permanent magnet.
As shown in FIG. 14, the valve gear 106 has the inner periphery, in which a fitted hole 110 is fitted onto a fitting part, which is provided to one end of the shaft 102. In the intake control device, flatted round portions 111, 112 are formed on the outer periphery of the fitting part of the shaft 102 and on the inner periphery of the fitted hole 110 of the valve gear 106. Thereby, the throttle valve, the shaft 102, and the valve gear 106 define a predetermined relative angle, and the shaft 102 and the valve gear 106 are restricted from rotating relative to each other. The valve gear 106 is joined to one axial end (the fitting part) of the shaft 102 by crimping the fitting part that extends through the fitted hole 110 to project from the end surface of the valve gear 106. A block-shaped full-closing stopper part 113 is integrally formed on the outer periphery of the valve gear 106. When the throttle valve is closed to a full-closing position, the full-closing stopper part 113 latches onto a block-shaped fully-closing stopper 107 provided integrally on the gearbox 103.
In the conventional intake control device, an adjustment structure needs to be provided in order to maintain a full-closing clearance defined between a throttle bore surface of the throttle body 101 and an outer peripheral end surface of the throttle valve at a desired clearance. The adjustment structure absorbs dispersion in dimensions of the throttle bore wall surface of the throttle body 101, dispersion in dimension of the outer periphery of the throttle valve, dispersion in assembling dimensions of the throttle shaft 102 and the throttle valve, and dispersion in assembling dimensions of the shaft 102 and the valve gear 106.
When the full-closing clearance is larger than a desired clearance, an amount of leakage air, when the throttle valve is in the full-closing position, increases. As a result, idling rotating speed may increase, and fuel consumption may increase. When the full-closing clearance is smaller than the desired clearance, the outer peripheral end surface of the throttle valve interferes with the throttle bore surface of the throttle body 101 in the vicinity of the full-closing position of the throttle valve. As a result, the throttle valve may cause seizure with the throttle body 101. In this case, the throttle valve may not normally perform opening and closing motions, and the amount of intake air cannot be properly controlled in the vicinity of idling opening degree.
Conventionally, an adjustment screw 109 is provided to project from the end surface of the fully-closing stopper 107 for adjustment of the full-closing position. The adjustment screw 109 is manually adjusted in length of an abutting part thereof, so that dimensions of respective parts and dispersion in assembly are absorbed. Thereby, a full-closing clearance is maintained at a desired clearance, so that an amount of leakage air is properly adjusted, when the throttle valve is in the full-closing position. As shown in FIGS. 13, 14, the adjustment screw 109 is screwed into the fully-closing stopper 107 of the gearbox 103 for defining full-closing opening degree. However, in this structure, the number of components increases, and adjusting the full-closing opening degree takes long, so that manufacturing cost increases. The adjustment screw 109 may be moved out of the adjustment. In this case, the dimension of the full-closing clearance may be changed from the desired full-closing clearance. When the adjustment screw 109 is sealed, the adjustment screw 109 may be restricted from being moved out of adjustment. However, manufacturing cost may increase due to the sealing work.
A magnetism detecting element may be used for a throttle sensor that detects the throttle opening degree. Specifically, a permanent magnet is fixed to the inner periphery of the valve gear 106, and a non-contact type magnetism detecting element is fixed to a sensor cover. The non-contact type magnetism detecting element generates electromotive force in response to a magnetic field generated by the permanent magnet. The sensor cover, which is separate from the throttle body 101, closes an opening side of the gearbox 103. In this structure, the rotating position of the permanent magnet relative to the magnetism detecting element may vary depending upon the adjusted position of the adjustment screw 109. Therefore, an adjustment structure needs to be constructed on the sensor cover, to which the magnetism detecting element is fixed, and an output adjusting function needs to be provided for the magnetism detecting element to adjust an output signal. Accordingly, adjusting both the adjustment structure and the output adjusting function takes long, and manufacturing cost may increase.